172
votes
Accepted
Why are IPv4 addresses running out?
The IPv4 Address Shortage
According to Vint Cerf (the father of IP), the IPv4 32-bit address size of was chosen arbitrarily. IP was a government/academic collaborative experiment, and the current ...
- 98.7k
82
votes
Accepted
Why do we need IPv6?
Two things are getting confused here:
classful addressing vs CIDR
Masquerading / NAT
Going from classful addressing to Classless Inter Domain Routing (CIDR) was an improvement that made the address ...
- 6,720
40
votes
Accepted
What is the difference between 0.0.0.0 and a loopback IP address?
The statement:
The IP address 0.0.0.0 [...] means ‘‘this network’’ or ‘‘this host.’’
is misleading. It is not a "or" but "This host on this network."
From RFC1122:
{ 0, 0 }
...
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38
votes
Why are IPv4 addresses running out?
Ron Maupin's answer gives a brilliant overview of the IPv4 shortage, but I'd like to address this part of your question:
Why can't a city (for example) have just one IP address and all homes in ...
- 480
33
votes
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Why are IP addresses given to each interface and not device? What would the implications of that be?
Connecting an interface to a network makes it a part of that network. Therefore, the IP address is a property of the connection, not the host.
Likewise, a host can have many network connections and ...
- 82.6k
33
votes
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What stops someone from configuring their network with IP addresses they do not own?
Most likely if they're a big university they are their own ISP, using BGP to connect their network to the internet via a number of upstream networks.
Nothing stops them from using IP addresses they ...
- 17k
27
votes
How do you calculate the prefix, network, subnet, and host numbers?
Part 1 of 2
IPv4 Math
With an IPv4 address and the network mask, the network mask length, or host mask, you can calculate the Network Address, Broadcast Address, Total Addresses, Usable Addresses, ...
- 98.7k
22
votes
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What is Link-local addressing?
I never seen 169.254/16 working in IPv4.
A PC automatically acquires a 169.254.x.x/16 address if it does not receive an IP address from a DHCP server. If you disable the DHCP server on your home or ...
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22
votes
Does every host on the LAN share the same ARP table, or do hosts keep them individually?
Actually, every interface in a device has its own ARP table. A host could have several ARP tables (one for each interface it has). ARP tables are not shared between hosts, or even among interfaces in ...
- 98.7k
22
votes
Difference between :: and ::1
:: is the unspecified address (0:0:0:0:0:0:0:0), and it is only used in packets as the source address of a host that does not yet have an address and is trying to get an address assigned. What you see ...
- 98.7k
21
votes
How do you calculate the prefix, network, subnet, and host numbers?
Continued from Part 1...
Part 2 of 2
Subnet IPv4 Networks
Subnetting a network is creating multiple, longer networks from a network address and mask. The basic idea is that you borrow high-order ...
- 98.7k
21
votes
Is `0.0.0.0/1` a valid IP address? If so, what does it indicate?
Zac is muddying the waters by excluding 0.0.0.0/8 and 127.0.0.0/8. While addresses in those two prefixes should never appear on the wire, 0.0.0.0/1 does cover them. The slash notation works the same ...
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20
votes
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Does anycast addressing add additional latency in any way?
Does anycast addressing, in itself, add any additional latency to
network connections?
No.
one using unicast and the other using anycast
Anycast is unicast. It is just that the same network is ...
- 98.7k
19
votes
Accepted
Why are there 3 ranges of private IPv4 addresses?
Back when the RFC for private addressing was proposed, classful addressing was still common. The reasons for the three address ranges are found in RFC 1918, Address Allocation for Private Internets:
...
- 98.7k
19
votes
Accepted
IPv4 Segment 100.64.0.0/10
The 100.64.0.0/10 address block is not private address space; it is shared address space. This is spelled out in RFC 6598, IANA-Reserved IPv4 Prefix for Shared Address Space (I highlighted the ...
- 98.7k
19
votes
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What are common sizes to split a /29 - /32 IPv6 subnet?
Some simple guidelines that work most of the time:
Dividing your /29
The standard size of your allocation from RIPE NCC is a /32
A /32 is a well-accepted prefix size in the global routing table
You ...
- 6,720
19
votes
Accepted
What happens when a subnet reaches capacity?
A subnet (network) is really just a collection of contiguous addresses within a binary mask. It is simply a logical way to divide address block. If you run out of addresses in a network (subnet), then ...
- 98.7k
19
votes
Accepted
Is there anything stopping me from using Class A addresses on my own network?
As long as you are translating your "15.0.0.0" address space to something unique on the Internet that doesn't overlap, things will "work fine".
However, you won't be able to ...
- 14.9k
17
votes
Why are IP addresses given to each interface and not device? What would the implications of that be?
It would not be enough.
Suppose I have a computer with three interfaces: eth0 (wired Ethernet), wlan0 (wifi), and vboxnet0 (virtualbox). One of the interfaces is connected to an internal network, one ...
17
votes
Accepted
Why the first octet of a MAC address always end with a binary 0?
You may notice that two least-significant bits of the most-significant byte of a 48-bit MAC address are usually set to 0 (as in all your examples). There are two flags in the most-significant byte of ...
- 98.7k
16
votes
Why do we need IPv6?
The Internet Protocol (IP) was designed to provide end-to-end connectivity.
The 32 bits of an IPv4 address only allow for about 4.3 billion unique addresses. Then you must subtract a bunch of ...
- 98.7k
16
votes
Why do we need MAC Address if we can uniquely identify each machine with an IP Address
There is a historical reason for this, as @ronmaupin alludes to.
In small networks, you don't need a layer 3 protocol. All the devices are directly addressable, so layer 2 addresses work fine. As ...
- 67.1k
16
votes
Why are IPv4 addresses running out?
Right now, every home has its own IP address. Why can't a city (for example) have just one IP address and all homes in this city would just be on a private network of that city?
Exactly this is ...
- 2,346
16
votes
Accepted
Is `0.0.0.0/1` a valid IP address? If so, what does it indicate?
0.0.0.0 is no valid IP address, regardless of prefix length. 0.0.0.0/0 as prefix matches any address, so it's used for the default route. Also, 0.0.0.0 is the unspecified address used in many APIs, ...
- 82.6k
14
votes
Accepted
What would happen to Ping if two PCs have same IP address with same Subnet Mask on same network?
Actually, the ping gets sent to a layer-2 address if they are on the same LAN. Assuming ethernet, the sending host may have a MAC address in its ARP cache, and the pings gets sent to the host with ...
- 98.7k
14
votes
Accepted
How do routers on the backbone avoid IP address conflicts?
The RIRs assign addressing to the ISPs. An ISP not following the rules will quickly find itself ostracized and cut off from the rest of the Internet.
IANA owns the addressing and assigns each of the ...
- 98.7k
14
votes
Why can I send 127.0.0.1 to 127.0.0.0 on my network?
we changed our FW so that the fixed IP addresses are 127.0.0.0 and 127.0.0.1.
Generally, that's a really bad idea. It is in violation of RFC 1122:
(g) { 127, <any> }
...
- 82.6k
13
votes
What is the difference between 0.0.0.0 and a loopback IP address?
If I am correct, a loopback IP address refers to the current host.
No. Traffic sent to a loopback address loops back inside the host. You can send traffic to a loopback address as the destination ...
- 98.7k
13
votes
Accepted
What are the negative impacts of using non RFC1918 addresses on a private network?
If those devices will actually never access the Internet, then the devices themselves will be fine, however there's still some potential issues:
what about other system that must communicate with ...
- 19.5k
Only top scored, non community-wiki answers of a minimum length are eligible